WINFIELD, Mo.  With a few days to go before the last stretch of the bloated Mississippi River reaches its crest, people toiled around the clock Monday to reinforce levees already strained and saturated from the pressure of the rising water.

Officials in Lincoln County asked for volunteers to help fill 50,000 sandbags to fortify the 2 1/2-mile-long Pin Oak levee, an earthen berm that was so waterlogged that it was like "walking on a waterbed," said county emergency management spokesman Andy Binder. Federal officials said they couldn't be sure it would survive through the river's crest at Winfield later in the week.

"They have a serious condition on their hands," Travis Tutka, the U.S. Army Corps of Engineers chief of dam safety, said late Monday afternoon. "This will be quite a test of that levee."

If it breaches, the river will swamp 100 homes in east Winfield, as well as 3,000 acres of farm fields, several businesses and a city ballpark. A muskrat burrowed a hole in the soft ground during the night, releasing a geyser of water, and officials said it took nearly six hours to choke off the leak.

"There is no guarantee of performance, but we're fighting the good fight," Tutka said.

Only a handful of residents remained in Winfield on Monday, after emergency workers went door to door urging them to evacuate. Among the holdouts was Sherman Jones, 56, who was all alone in his house except for his dogs, Mugsy and Junior.

"There is no place to go but the high school. I am not going to leave 'til my feet are wet," Jones said. "It's been a rough year, but we'll get through it."

Elsewhere in the hard-hit county a few dozen miles north of St. Louis, National Guard soldiers patrolled levees looking for soft spots.

Down river in Grafton, Ill., Mayor Richard Mosby said about 20 homes and businesses were flooded  but no more were expected to be affected if the Mississippi crests as forecast just a few inches above Monday's level.

The river's crest was not expected to reach Grafton and Winfield until Thursday or Friday, according to the federal river forecast issued Monday afternoon.

Upriver, where the river already had crested, officials nervously stood watch Monday as they waited for the danger to recede. Lt. Gen. Robert Van Antwerp, the Army Corps' chief of engineers, toured Clarksville on Monday afternoon and said he was most concerned about agricultural levees up and down the river.

"I think what they have is holding well," Van Antwerp said. "Now, it's a matter of getting the water off of it."

Not far from the Iowa state line, the river was down a few inches at Canton after cresting Sunday at 27 feet  less than a foot short of the record set during the Great Flood of 1993. Jeff McReynolds, the city's emergency management director, said a voluntary evacuation request remained in place in the town of roughly 2,500.

"We were right up there to our nostrils for about 24 hours," McReynolds said. "The concern from our operations center is they (residents) have seen the crest, and think the river has come down and want to move back into their homes."

Illinois Emergency Management Agency officials said National Guard soldiers, prison inmates and others kept piling sandbags Monday on the Sny levee, a 52-mile barrier near Quincy, Ill., as the river crested Monday and started to recede.

Down river from Quincy, the levee at Hannibal, Mo., was holding the slowly falling river out of the boyhood hometown of Samuel Clemens, who wrote as Mark Twain. Marion County Emergency Management Director John Hark said the city was already planning for its National Tom Sawyer Days, the early July festival celebrating Twain's work.

Hark said that with the river dropping, he could focus on other things that might discourage tourists  such as high gas prices.